Hydraulic systems are often used to control the operation of hydraulic actuators of work machines. These hydraulic systems typically include valves, arranged within hydraulic circuits, fluidly connected between the actuators and pumps. These valves may each be configured to control a flow rate and direction of pressurized fluid to or from respective chambers within the actuators. In some instances, multiple actuators may be connected to a common pump. Actuation of one such actuator may cause undesirable pressure fluctuations within one or more of the hydraulic circuits fluidly connected to the common pump. Also, actuation of one actuator may require a significantly higher pressure from the pump than actuation of other actuators either independently or simultaneously.
One method of reducing pressure fluctuations in hydraulic systems is described in U.S. Pat. No. 5,878,647 (“the '647 patent”) issued to Wilke et al. The '647 patent describes a hydraulic circuit having two pairs of solenoid valves, a variable displacement pump, a reservoir, and a hydraulic actuator. One pair of solenoid valves includes a head-end supply valve and a head-end return valve and connects a head-end chamber of the hydraulic actuator to either the variable displacement pump or the reservoir. The other pair of solenoid valves includes a rod-end supply valve and a rod-end return valve and connects a rod-end chamber of the hydraulic actuator to either the variable displacement pump or the reservoir. Each of the four solenoid valves is associated with a different pressure compensating valve to control a pressure of fluid between the associated valve and the actuator.
Although the multiple pressure compensating valves of the hydraulic circuit described in the '647 patent may reduce pressure fluctuations within the hydraulic circuit, they may establish high pressure drops when reducing the output pressure of the pump to the desired pressure for actuation of the hydraulic actuator. These high pressure drops may be unnecessary to operate the hydraulic actuator as desired, and may reduce the available flow of pressurized fluid by unnecessarily establishing a high output pressure of the pump, and/or may reduce the efficiency of the hydraulic circuit by requiring unnecessary energy from a power source operably driving the pump. Additionally, because the hydraulic circuit may have a plurality of hydraulic actuators, the actuator that establishes the highest output pressure from the pump may change depending on external loads on the plurality of actuators and/or operator inputs. As such, a system configured to lower pressure requirements may need to be flexible to adjust to the changing external loads and/or operator inputs.
The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above.